From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:32898) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QSAzh-0002OL-WF for qemu-devel@nongnu.org; Thu, 02 Jun 2011 12:43:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QSAzg-0003n0-KT for qemu-devel@nongnu.org; Thu, 02 Jun 2011 12:43:37 -0400 Received: from mail-yx0-f173.google.com ([209.85.213.173]:35453) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QSAzg-0003mt-8i for qemu-devel@nongnu.org; Thu, 02 Jun 2011 12:43:36 -0400 Received: by yxk8 with SMTP id 8so479649yxk.4 for ; Thu, 02 Jun 2011 09:43:35 -0700 (PDT) Sender: Richard Henderson Message-ID: <4DE7BDB4.1060601@twiddle.net> Date: Thu, 02 Jun 2011 09:43:32 -0700 From: Richard Henderson MIME-Version: 1.0 References: <1307027562-3460-1-git-send-email-david@gibson.dropbear.id.au> <1307027562-3460-2-git-send-email-david@gibson.dropbear.id.au> In-Reply-To: <1307027562-3460-2-git-send-email-david@gibson.dropbear.id.au> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 01/14] Generic DMA memory access interface List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Gibson Cc: qemu-devel@nongnu.org, eduard.munteanu@linux360.ro On 06/02/2011 08:12 AM, David Gibson wrote: > + err = iommu->translate(dev, addr, &paddr, &plen, is_write); > + if (err) { > + return NULL; > + } > + > + /* > + * If this is true, the virtual region is contiguous, > + * but the translated physical region isn't. We just > + * clamp *len, much like cpu_physical_memory_map() does. > + */ > + if (plen < *len) { > + *len = plen; > + } > + > + buf = cpu_physical_memory_map(paddr, &plen, is_write); > + *len = plen; > + > + /* We treat maps as remote TLBs to cope with stuff like AIO. */ Oh, that reminds me. There's a bug here in Eduard's original: PLEN is set to the maximum length of the transfer by the translate function. What we do *not* want is to pass a very very large region to cpu_physical_memory_map. The effects of this are hard to see with the AMD IOMMU, since it is entirely page based and thus PLEN will be increased by no more than 4k, but Alpha IOMMUs have direct-mapped translation windows that can be up to 128GB. I'm unsure whether I prefer to force the translator function to never increase PLEN (which is what I implemented in my own branch) or whether all callers of the translate function must be aware that the returned PLEN can increase. r~